Puming system

ABSTRACT

A pump unit which includes a pipe, a flexible bladder inside the pipe, an operating volume between an outer surface of the bladder and an opposing inner surface of the pipe, a valve arrangement to introduce pressurised water into the operating volume and to allow pressurised water to flow from the operating volume and another valve arrangement to allow slurry to flow into the interior of the bladder as water is expelled from the operating volume and to—allow slurry to flow from the bladder when water is introduced into the operating volume.

BACKGROUND OF THE INVENTION

This invention relates to pumping apparatus.

The apparatus of the invention is suitable for pumping media such as slurries. The invention is described hereinafter with reference to this application, i.e. to the pumping of a slurry, but this is exemplary only and is non-limiting.

The specification of international application No. PCT/ZA2009/000071 describes a pumping system which makes use of two pressure vessels. Each vessel is cylindrical with hemispherical ends and is orientated so that its longitudinal axis is vertical. Nozzles are provided at upper and lower ends of the vessel.

Each vessel contains an elongate flexible bladder which is aligned with the longitudinal axis. The bladder, at an upper end, has an open neck which is sealingly engaged with the upper nozzle to define a first volume within the bladder and a second volume between the bladder and an opposing inner surface of the wall of the vessel.

Slurry is fed gravitationally via a first one-way check valve through the bottom nozzle to fill the second volume. This action displaces the bladder inwardly around the longitudinal axis and, in so doing, water inside the bladder is displaced from the bladder through the upper nozzle. A measured volume of water under pressure from a pump is then introduced into the bladder through the open neck. The bladder expands and, in so doing, the slurry in the second volume is expelled through the bottom nozzle via a second one-way check valve into a discharge line.

While one vessel is being filled with water, to pump out its slurry contents, the other vessel is being refilled with slurry and displaces its water to an inlet of the pump.

The process continues indefinitely in this way with the pumping operation being changed from one pressure vessel to the other to produce a smooth discharge flow of slurry.

During the period that water is being pumped into the bladder of one vessel the other vessel must be depressurised and the slurry flow rate must be increased, from a zero value, in order to fill the second volume. Thereafter the slurry flow rate must be progressively decreased to zero. The pressure in the vessel is then raised to an operating value in readiness for the changeover of the pumping operation. A few seconds of waiting time, known as “overlap time”, are then allowed before the switchover is implemented.

The various functions in the second vessel, which are essential for effective pumping operation, are time consuming and place a limit on the rate at which the bladder in each vessel is filled with water i.e. the slurry pumping rate is restricted.

Apart from the aforementioned flow constraint, the pumping system described in the international specification has some further drawbacks.

The vessels are expensive to manufacture. The hemispherical ends are complex and costly to form and the nozzles, at the upper and lower ends, are forgings which are machined. This is expensive and requires substantial production time. As the diameter of each vessel increases cyclic hoop stresses which are generated in use by the pumping operation increase and the thickness of the wall of the vessel must be increased to be able to handle the hoop stress. An internal surface of the vessel which is in contact with the slurry requires a protective lining to resist abrasion.

Each vessel is vertically aligned so that slurry can flow into and out of the second volume through the lower nozzle. This results in a tall structure with a high centre of gravity which, in turn, calls for an extensive structural support framework as well as substantial civil foundations for stability, particularly in regions which are subject to seismic or similar events.

If the pumping system is assembled in a building then sufficient clearance must be allowed above the structure for a crane which is used to assemble the vessels. The pump assemblies are large and, when transported, are regarded as abnormal loads and the relevant regulations then come into play.

High level service platforms and stairways must be provided, in conformance with safety requirements, so that the vessels and associated valves can be accessed for maintenance purposes. In addition, the system must have a lifting device which can extract and insert the bladders, and valve tubes through the upper nozzle, as service is required.

As slurry is gravity-fed into the system, the level of a slurry supply tank must be higher than the top of the pressure vessels.

In general a substantial amount of on-site work is required to install and commission the pumping system. A water pump and motor unit must be installed separately on appropriate foundations; a VSD (variable speed drive) must be installed in an air-conditioned room on site; and stairways and service decks must be assembled on site as they are too bulky to be transported in an assembled condition.

An object of the present invention is to provide pumping apparatus which aims to address, at least partly, a number of the aforementioned aspects.

SUMMARY OF THE INVENTION

The invention provides in the first instance a pump unit which includes:

-   -   (a) an elongate tubular housing with an inner bore, a first end         and an opposing second end,     -   (b) an elongate flexible bladder of tubular form with an         interior, an inlet, at one end of the bladder, to the interior,         and an outlet, at an opposing end of the bladder, from the         interior, wherein the bladder is positioned Inside the bore with         the bladder in sealing engagement with the housing at opposed         ends of the bladder whereby the inlet is in communication with         the first end of the housing, the outlet is in communication         with the second end of the housing and an operating volume of         variable size is formed between an outer surface of the bladder         and an opposing inner surface of the housing,     -   (c) a port for an actuating fluid which is provided on the         housing in communication with said operating volume,     -   (d) an inlet non-return valve connected to the first end of the         tubular housing,     -   (e) an outlet non-return valve connected to the second end of         the tubular housing,     -   (f) a first control valve for controlling the flow of the         actuating fluid through the port into the operating volume, and     -   (g) a second control valve for controlling the flow of the         actuating fluid from the operating volume through the port.

In one form of the invention the pump unit includes metering means for metering the flow of the actuating fluid through the port. This may be done on a volume basis. The metering means may comprise a bi-directional flow meter.

The metering means may be connected to a controller and the controller may monitor the volume of actuating fluid which flows into the operating volume, and out of the operating volume.

The elongate tubular housing may be formed in any appropriate way and preferably, in this respect, use is made of a pipe of a suitable specification. Opposing first and second ends of the pipe may be flanged.

The port may be formed through a wall of the pipe.

The bladder, which is of tubular form, may be made from an appropriate material e.g. rubber.

Opposing ends of the bladder, i.e. at the inlet and the outlet, may be sealingly engaged with respective flanges at the first and second ends of the pipe.

The inlet non-return valve may be adapted to allow the medium which is to be pumped to move, preferably under gravity action, into the interior of the bladder.

The outlet non-return valve may be adapted to allow the medium which is pumped to pass, under pressure, into a discharge line.

The actuating fluid may be of any suitable kind but, preferably, is water. Water flow into, and out of, the operating volume is monitored by the bi-directional water meter i.e. the meter can measure the quantity of water which flows through it in one direction and then in an opposing direction. This is important as the pumping operation, in one embodiment of the invention, is based on volume measurements, and not on time or other measurements, to obtain a precisely controlled pumping sequence.

In a variation of the invention the metering means (in the preceding specific example the bi-directional flow meter) is not employed, and one or more sensors are used instead to control the flow of the actuating fluid. Each sensor is positioned at a chosen location to obtain an indication of the position of the bladder relative to the tubular housing at or near the chosen location. Each sensor may be of any suitable kind. For example, a sensing function may be provided by locating a magnet on or in the bladder and using a Hall-effect device or a similar appliance to detect the proximity of the magnet, or to detect when the magnet is moved away from a sensing region of the Hall-effect device or appliance. A capacitive sensing system may also be employed. The capacitance sensed by an appropriate detector varies as the bladder approaches a location at which the sensor is positioned and this is used as an indication of the position of the bladder relative to the tubular housing in an area which is at, or adjacent, the sensor. In another approach a metallic insert is positioned on or otherwise attached to the bladder and as the bladder moves the insert moves by a corresponding amount and this movement can be detected by an appropriate sensor e.g. a magnetic device which responds to the presence or absence of the metallic insert. These examples are exemplary only and are non-limiting.

In a preferred form of the invention multiple sensors are used with a first sensor being employed to detect when the bladder is full and a second sensor being employed to detect when the bladder is effectively emptied i.e. its contents are depleted. At least one intermediate sensor (a third sensor) may be positioned at a location which is between the first and second sensors to detect when a predetermined bladder configuration has arisen e.g. when the bladder (say) is half full. This can be used, as is further described hereinafter, to ensure a smooth and controllable sequencing operation when a plurality of the pump units are employed.

One or more sensors (apart from the sensors mentioned) may be used as failsafe devices. For example, a sensor can be used to ensure that when a bladder is emptied, i.e. its contents are expelled from the bladder, that further operation does not take place which could cause damage to the bladder.

A particular benefit of this approach, i.e. the use of the sensors, is that it enables the bi-directional flow meter to be eliminated. The flow meter is expensive and requires careful operation to ensure its integrity of functioning. Sensors of the kind referred to on the other hand are robust and relatively low-cost devices. As the bladder is constrained within the tubular housing and is secured to the housing at its inlet and outlet, any possible movement of the bladder relative to the housing during operation is limited essentially to movement between a fully collapsed configuration and a fully expanded configuration. Because the movement of the bladder between these configurations is predictable it is possible to make use of the sensors, as indicated, to detect, in a reliable manner, movement of the bladder. Effectively this means that when the pump unit is employed it can be controlled by signals which are generated in response to the bladder movement as opposed to the other embodiment in which control signals are generated in response to signals determined by metering the volume flow of the actuating fluid.

The invention extends, in the second instance, to pumping apparatus which includes three pump units, each pump unit being of the aforementioned kind, wherein the three pump units are mounted substantially parallel to each other on supporting structure which preferably has outer dimensions which are substantially the same as the outer dimensions of a conventional shipping container.

With the supporting structure on a level surface the first ends of the tubular housings are preferably elevated so that each housing then slopes downwardly over the length of the supporting structure towards its second end.

The first non-return valves and a first manifold may, in use, be positioned so that they lie outside the supporting structure. Similarly the second non-return valves and a second manifold may, in use, lie outside the supporting structure.

The use of three pump units, under the control of a suitable controller, enables the medium to be pumped continuously without meaningful pressure variations. Of substantial importance is the fact that the pumping rate is approximately twice the pumping rate of the pumping system described in the aforementioned international patent application. In other words, by using three pump units instead of two pump units, a hundred percent increase in pumping rate is achieved. The pumping rate can match the rate at which the medium to be pumped flows into the pumping apparatus. Typically the medium is a slurry which flows under gravity action to the pumping apparatus.

In general terms the increased pumping rate results from the sequenced operation of the pump units which can each work at a maximum rate for there is no need to interrupt the pumping rate to allow for sufficient time within which a second pump unit can be readied for operation, as is the case with the pumping system in the international application. Thus, in the three pump unit arrangement the medium is pumped from a first pump unit and, at the same time, a second pump unit is prepared for pumping. Thereafter the pumping operation is transferred from the first pump unit to a third pump unit and pumping from the third pump unit takes place, the preparation of the second pump unit is completed and the preparation of the first pump unit for pumping operation is commenced. The pumping operation is then transferred to the second pump unit, the preparation of the first pump unit is completed and the preparation of the third pump unit for pumping operation is commenced.

The aforementioned process continues in this way, under the control of the control unit, indefinitely. The pumping sequence is controlled by monitoring the volume of the actuating fluid (typically water) which flows into, and subsequently out of, each operating volume. In the first embodiment use is made of bi-directional flow meters to monitor these water volumes. This approach practically eliminates the prospect of incremental creep or overlap, due to inaccurate water measurements, causing a malfunction in the pumping operation. On each count cycle each flow meter is reset to a zero value. Subsequently the flow meter counts the volume of water which flows into the pump unit and thereafter out of the pump unit.

However, in the second embodiment the bi-directional flow meters are not employed. Instead, the sensors referred to are used. These sensors also monitor the passage of the actuating fluid which flows into, and subsequently out of, each operative volume. Arguably the monitoring accuracy of the sensors is not of the same order of what is achieved through the use of the flow meters. However, when the sensors are used precise accuracy is not called for. Instead what is required is an indication (and this can be done within an acceptable degree of tolerance) when each bladder has been filled with a medium which is to be pumped and when each bladder has been emptied. Additionally, for assistance in controlling the sequencing operation of the various pump units at least one intermediate sensor is used to determine the condition of a bladder between full and empty.

Control of the pumping process is readily effected. In the first embodiment, as slurry flows into a bladder water is expelled from the operating volume between an outer surface of the bladder, and an inner surface of the pipe in which the bladder is located.

The water which flows out is monitored by the respective water meter. When the water flow stops this is indicative that the bladder has been filled with slurry. A count of the water meter is then reset to zero in the controller, typically a PLC. In practice pulses from the water meter are generated at regular volume intervals, typically one pulse for 10 litres of water. When the slurry is to be discharged from the bladder water is introduced into the operating volume.

Water flow is diverted from a first pump unit to a second pump unit. Before such diversion takes place the pressure in the operating volume of the second pump unit is increased to the prevailing operating pressure. Consequently, when the water flow is diverted to the second pump unit, there is substantially zero pressure difference between the pressure of the incoming water and the water in the operating volume and the diversion takes place without generating pressure spikes or the like.

As indicated, an equivalent and equally effective process can be implemented by replacing the water meters with the sensors. The sensors provide equivalent information to that generated by the water meters, namely an indication of when each bladder has been filled with slurry, an indication when each bladder has been emptied, and an indication of an intermediate position (e.g. that the bladder is half-full) at which suitable sequencing actions can be implemented to ensure a smooth operation.

Preferably, the supporting structure used for the pump units is in the nature of a conventional container. This substantially facilitates assembly of the pumping apparatus, its transport to a usage site and, at the usage site, installation and commissioning thereof. Site preparation requirements are minimised. Typically, at an installation site, the first and the second manifolds and the attendant one way and control valves, which are separately transported, e.g. in a second container, are connected to the pump units. The supporting structure (container) used for the pump units can have mounted to it gantries or jibs to facilitate assembly processes on site.

Depending on the size of the pump units a conventional 40 ft container could be employed to accommodate the pump units. However, a container of this size can be awkward to handle and transport, particularly if the arrangement is to be used in a remote region. It is therefore possible to use two smaller containers, say, each the size of a conventional 20 ft container, and to form the pump units in respective half sections. When the smaller containers are assembled on site in an abutting relationship, the pump unit sections can be coupled together, as required, to form an integral arrangement.

In the aforementioned arrangement the pump units are placed in structure which, as noted, is in the nature of a conventional shipping container. The pump units are thus fairly close to the ground. Gravity flow of slurry into each pump unit, as required, during the pumping process can take place from a slurry supply tank which thus need only be higher than the pump units. In other words it is not necessary to have a slurry supply source a substantial height as is the case in the pumping system in the aforementioned PCT application.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of examples with reference to the accompanying drawings in which:

FIG. 1 is a view in perspective of three pump units, included in pumping apparatus according to the invention, mounted to support structure which is in the form of a conventional large container which has a standard length, height and width,

FIG. 2 is a view in elevation of the arrangement shown in FIG. 1,

FIG. 3 is a plan view of the arrangement in FIG. 1,

FIG. 4 is an end view of the arrangement, in the direction of an arrow marked 4 in FIG. 3.

FIG. 5 illustrates in perspective a bladder used in a pump unit,

FIG. 6 is a schematic view from one side and in cross-section depicting the mounting of the bladder of FIG. 5 to a pipe,

FIG. 7 is a view from one side of the pump units (i.e. similar to what is shown in FIG. 2) with first and second manifolds and non-return valves connected to the pump units,

FIG. 8 is a side view on an enlarged scale and in section of part of a first manifold and an inlet non-return valve shown in FIG. 7,

FIG. 9 is similar to FIG. 8, but showing a portion of a second manifold and an outlet non-return valve;

FIG. 10 has four images namely FIG. 10A which shows a slurry-in manifold, FIG. 10B which shows a water-in manifold; FIG. 10C which shows a water-out manifold; and FIG. 10D which shows a slurry-out manifold;

FIG. 11 illustrates in plan, and from one side, respectively, an assembled pump unit;

FIG. 12 illustrates support structure in the form of two conventional small containers, each of a standard length, height and width, which can be interconnected to form an arrangement similar to that shown in FIG. 1; and

FIG. 13 is a schematic representation of an alternative embodiment of the invention in which sensors and not water meters are used to control the individual pump units to ensure an effective sequencing operation.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 to 4 are different views of three pump units 10, 12 and 14 respectively which are mounted to supporting structure 18.

The supporting structure is shown in skeletal form. Typically the supporting structure is embodied in, or constituted by, a conventional transport container i.e. the structure 18 has a length L, a height H and a width W (FIG. 1) which conform to the dimensions of a conventional container. Sides of the supporting structure are not closed—this facilitates access to equipment mounted to the structure.

The construction of the unit 14 only is described hereinafter. The units 10 and 12 are similar to the unit 14.

The unit 14 includes an elongate tubular housing 24 in the form of a pipe which is made to a suitable specification and which has a length 26 and a diameter 30. The pipe 24 has a first end 34 and an opposing second end 36. Each end is provided with a respective flange 40, 42.

Near the first end 34 (FIG. 2) the pipe 24 is formed with connecting structure 46 which includes an inlet port 48. A water supply pipe 50 is connected to the port 48. A bi-directional water meter 52 is connected in line to the pipe 50. At an end remote from the port 48 the pipe 50 is connected to a control valve 54 which is coupled to a water-in manifold 54A and to a control valve 56 which is coupled to a water-out manifold 56A.

The pipe 24 slopes downwardly, from the left to the right in FIG. 2, when the supporting structure (container) 18 is on level ground.

The pump units are assembled, as indicated, under factory conditions. The supporting structure and the pump units can then be shipped using conventional container transport techniques to an installation site.

A second container, not shown, houses a control unit 60 such as a PLC, a VSD, an air-conditioner, a pump set, a store and a site office, three first non-return valves 62 (FIG. 8), and three second non-return valves 64 (FIG. 9) (one of each for each pump unit), a slurry-in manifold 66 (FIG. 10A), a slurry-out manifold 68 (FIG. 10D), the water-in manifold 54A (FIG. 10B) and the water-out manifold 56A (FIG. 10C). The second container is also shipped, with its contents secure inside, to the installation site. At this site use can be made of jibs or cranes 74 which are fixed to the first container (FIG. 7), i.e. to the supporting structure 18, to assist in mounting the manifolds and valves to the respective ends of the pipes of the three pump units.

FIG. 6 illustrates in cross-section, and from one side, the pipe 24. Positioned inside the pipe is a bladder 76 which is made from a flexible material such as rubber and which is shown in FIG. 5. The bladder is of elongate tubular form and has flange formations 78 and 80 at opposed ends. These flange formations respectively overlie faces of the flanges 40 and 42 and, in use, are clamped between a mating flange 84 of the non-return valve 62 and a mating flange 86 of the non-return valve 64, respectively. The bladder has a nominal diameter 30A which is the same as the diameter 30. A first, open end 76A of the bladder 76 is in direct communication with the first end of the pipe 24, and an opposing, second, open end 76B of the bladder is in direct communication with the second end of the housing. An operating volume 88, of variable size, is formed between an inner surface 90 of the pipe 24 and an opposing outer surface 92 of the bladder 76. The inlet port 48 is in direct communication with the operating volume 88. The bladder is reinforced e.g. by means of additional layers 94 of rubber or other material, over a portion of its length adjacent the flange 78. The reinforcing is adjacent the port 48 when the bladder is placed inside the pipe.

FIG. 8 shows from one side and in cross-section a portion of the inlet non-return valve 62 and the pipe 24. The port 48, which is an opening in a side wall of the pipe 24, is crossed by a grid structure 96 which, in use, prevents the bladder 76 from being forced into the water pipe 50, when the bladder is filled with slurry. The reinforcing layers 94 also assist in this respect.

The first end 34 of the pipe is connected via tubular structure 98 to the non-return valve 62 and the second end 36 is connected by means of tubular structure 102 to the non-return valve 64, see FIG. 9.

The three inlet non-return valves 62 associated with the respective pump units are connected at their inlets to the slurry-in manifold 66 shown in FIG. 10A. The three outlet non-return valves 64, associated with the respective pump units, are connected at their outlets to the slurry-out manifold 68 shown in FIG. 10D. This manifold is connected to a discharge line.

The slurry-in manifold 66 is connected to a slurry supply line 100 from a slurry supply source 102—see FIG. 7. An upper level of the slurry in the source is above the highest points of the bladder.

The inlets to the valves 54 of the three pump units are connected to the water-in manifold 54A shown in FIG. 10B. The outlets from the valves 56 of the three pump units are connected to the water-out manifold 56A shown in FIG. 10C.

The water meters provide data on water flow to the controller 60. The control valves 54 and 56 are responsive to signals from the controller 60 which functions in accordance with a proprietary algorithm to regulate the operation of each pumping unit.

Assume that the pumping apparatus is used to pump slurry at high pressure using an actuating fluid such as water which is drawn from a water tank 106 using a high pressure water pump 108.

The slurry is gravity-fed from the source 102, see FIG. 7, through the non-return valve 62 into the bladder of the pump unit 14. Water flows from the operating volume of that pump unit via the port 48 into the line 50 and, from there, through the control valve 56 to the water tank 106. This water is expelled by the pressure exerted by the slurry inside the interior of the bladder. Once the bladder is filled with slurry the size of the respective operating volume 88, for practical purposes, is zero. The quantity of water flowing out is monitored by the corresponding meter 52 and is recorded in the controller 60.

The quantity of water pumped into the volume 88 of the pump unit 14 is measured by the water meter and is controlled to be equal to the quantity previously expelled from the bladder and measured by the meter. The size of the operating volume 88 of the pump unit 14 is increased as this volume is pressurised. The volume of the bladder undergoes a corresponding decrease in size. Slurry is thus expelled from the bladder into the slurry-out manifold 68 through the respective one-way valve 64, and into the discharge line.

While the pump unit 14 is being used to pump slurry the second pump unit 12 is readied to ensure that there is no water in the operating volume of the second pump unit and that the bladder of the second pump unit is filled with slurry. The pressure prevailing in the operating volume 88 of the second pump unit is controlled via the controller 60 and is set to be equal to the pressure available from the water pump which is used to pump water into the pump unit. Effectively, the water in this operating volume is brought to an operating pressure by slightly opening the corresponding control valve 54. This is done at a time which is shortly before pumping from the pump unit 12 is to start. As the water is incompressible the amount of water which must be introduced into the operating volume 88, to raise the pressure therein to the desired level, is minimal.

Once the pump unit 14 has completed its pumping cycle, as determined by the measurements from the water meter, the water meter count held in the controller is set to zero. At this point water flow is diverted into the operating volume 88 of the second pump unit 12. The pumping operation is moved smoothly from the third pump unit 14 to the second pump unit 12 so that slurry is discharged from the bladder of the second pump unit via the corresponding non-return valve 64 into the slurry-out manifold 68 shown in FIG. 100. The diversion is done without producing any pressure spikes and without interrupting the slurry flow. The quantity of water which goes into the second pump unit 12 is monitored, as before, by the appropriate bi-directional water meter 52. This is an important aspect because, each time water is expelled from a pump unit, the volume of water is metered and controlled to be equal to the volume of water which previously flowed into the pump unit.

While the pump unit 14 is being operated and when switching takes place from the pump unit 14 to the pump unit 12, the pump unit 10 is readied for operation i.e. the operating volume 88 of the pump unit 12 is pressurised with water. Consequently, when the pump unit 12 has fully expelled its slurry, switching of the pumping cycle to the pump unit 10 can be accomplished with ease and without pressure spikes or flow interruptions. Before this happens and after it happens the pump unit 14 is readied for operation so that the pumping process can be continued by the pump unit 14.

In each pump unit, the corresponding bladder 76, at what in use is a lower end, has one or more metallic inserts 120, see for example FIG. 5. These inserts are embedded into the rubber or otherwise attached to the rubber from which the bladder is made. The pipe in which the bladder is located has a sensor 126 or a number of sensors which are responsive to the presence or absence of the inserts.

FIG. 6 illustrates somewhat schematically how the bladder is deformed when water is introduced into the operating volume 88. As water flows into the volume 88 the bladder, at an upper end, is compressed and an upper half of the bladder is forced onto a lower half of the bladder. With an increasing view of water into the volume 88 the bladder is collapsed over its length into a trough shape, lying on a lower half of the pipe 24—see the cross-sectional view in FIG. 6A. The collapse/compression should stop while the metal inserts 120 are still within range of the corresponding sensors 126. If the bladder is collapsed beyond this point then bladder can be damaged and the metal inserts to be moved away from the sensors. The provision of the metal plates thus acts as a backup in that, if a metal plate is separated from its corresponding sensor, this is immediately detected and a signal is sent to the controller 60 which automatically terminates the pumping operation.

FIG. 1 shows an arrangement wherein the pumping apparatus, which includes the three pump units, is mounted to supporting structure 18 which is in the form of a conventional large shipping container, typically with a length L equal to 40 ft. A container of this size can be awkward to handle and transport particularly if installation of the pumping apparatus is required at a remote site. To address this aspect, at least to some extent, use can be made of the structure shown in FIG. 11. The support structure 18 is divided into two sub-containers 18A and 188 respectively. Each sub-container is of the size of a conventional small shipping container which has a standard length of 20 ft. The pump units are divided into respective half sections i.e. each of the pipes 24 which comprise the housings for the pump units are divided into two sections and the sections are fitted with flanges 130 which enable the sections to be coupled together on site, when appropriate. Once this coupling has been effected each assembled pipe can have a corresponding bladder inserted into it.

In the embodiment referred to, use is made of bi-directional flow meters to provide an accurate measure of the volume of water flowing into each pipe 24 and out of each pipe 24. At the end of each measurement cycle, each flow meter is set to zero. These bi-directional flow meters are expensive and adequate safeguards should be implemented to ensure that they are not inadvertently damaged particularly in the robust and arduous conditions which may exist at an operational pumping site.

In a second preferred embodiment of the invention the flow meters are dispensed with. Instead, referring for example to FIG. 6, use is made of a plurality of sensors 132, 134 and 136 which are axially spaced apart to monitor the position of the bladder relative to the pipe 24 at each location at which a respective sensor is installed. The sensor 132 is close to the water inlet port 48. The sensor 136 is close to an opposing end of the pipe which is adjacent the slurry-out manifold 56A. The sensor 134 is positioned at a location which is between the sensors 132 and 136. Ideally a fourth sensor is employed. Effectively this is the same as the sensor 126 and it is used to ensure that if adequate switching of the pumping operation is not achieved through the sensors 132 to 136 and an undesirable condition arises due to the bladder being forced away from the inner surface of the pipe 24 at the end which is close to the slurry-out manifold, that the pumping operation can be stopped. This occurs as the sensor 126 detects movement of the bladder away from the opposing surface of the pipe.

The sensor 132 is, for example, in the nature of a Hall-sensor and is responsive to a magnetic field generated by one or more magnets 132A which are attached to a corresponding and opposing surface of the bladder. When the magnets are close to the sensor 132 a first output signal results but if the magnets move away from the sensor 132 a different signal is produced by the sensor 132. Similar arrangements are provided for the sensors 134 and 136 in that magnets 134A and 136A respectively are fixed at suitable locations to the bladder.

The sensors can be used effectively, in place of the water meters, as it has been realized that it is not necessary to obtain a precise measure of the volume of water which flows into and out of each pump unit provided that reliable and safe switching occurs at a determined position in a pumping sequence. Thus, if the sensors simultaneously detect respective magnetic fields this is a positive indication that the bladder has been filled with slurry. If the sensors 134 and 136 only are positive this is an indication that the bladder at the water inlet end of the pump unit has commenced its collapsing sequence. In the further collapsing of the bladder a stage is reached at which the magnets 134A move away from the sensor 134 and, again, this is clearly reflected in a change in the output signal from the sensor 134. A similar situation occurs when the magnets 136A move away from the sensor 136. Provided these indications are given reliably and consistently, in a repeatable manner, the signals can be used to effect control of the pumping apparatus which includes three pump units, much in the manner which has already been described wherein reliance is placed on the use of the water meters.

In this respect, reference is made to FIG. 13 which illustrates three pump units in each of which sensors are used in place of the water meters referred to. For the sake of convenience reference numerals which have been employed hereinbefore are again used in FIG. 13 to indicate like components. The water meters are of course absent from FIG. 13 which shows the sensors 132 to 136 for the three pump units as 132A, 134A and 136A, 132B. 134B and 1368, and 132C, 134C and 136C respectively. Water to the pump units is pumped from a source 140 by a pump 142 through a network 144 and is returned via a network 146. Slurry 150 from a source 152 is gravity fed to the pump units through a network 154 and as a result of the pumping operation is expelled into a slurry discharge line 156. In FIG. 13, the water inlets to the pump units are respectively marked WIA; WIB and WIC; the water outlets are marked WOA; WOB and WOC; the slurry inlets are marked SIA; SIB and SIC; and the slurry outlets are marked SOA; SOB and SOC. The operation of the pumping apparatus shown in FIG. 13 can be described, briefly, as follows:

-   -   1) each bladder is filled with slurry by opening the water-out         valves and water is fully expelled from each pipe into the water         tank. The water-out valves are then closed;

2) the water-in valve for the pump unit 14 is opened and the water pump 142 is then used to pump water into the operating volume 88 of the pump unit 14. The bladder starts collapsing as has been described in connection with FIG. 6 and moves away from the sensor 132C. the bladder progressively deforms until the sensor 134C is reached at which point the water-in valve on the pump unit 12 is caused to open slightly to pressurize the operating volume 88 of the pump unit 12;

-   -   3) when the sensor 136C detects movement of the bladder away         from the pipe, it is taken that all of the slurry has been         expelled from the bladder inside the pump unit 14. At this point         the water flow is diverted to the bladder in the pump unit 12;     -   4) when the sensor 136B is reached water is diverted to the pump         unit 10, which has previously been fully pressurized and a         similar sequence to what has been described in connection with         the pump unit 14 takes place with the pump unit 10;     -   5) when the water-in valve of the pump unit 14 is fully closed,         the controller causes the water-out valve of the pump unit 14 to         be opened. Slurry flows into the bladder of the pump unit 14 and         displaces the water from the operating volume 88 of the pump         unit 14. When the centrally positioned sensor 134C is closed the         controller causes the water-out valve to start closing slowly         until the valve is almost fully closed. When the sensor 132C is         closed the controller closes the water-out valve fully. This         process of controlling the flow of the water prevents water         hammer.

The sequence continues in this way with the operating volume of each pump unit being internally pressurized to a desired operating value before actual pumping takes place from that unit. This process effectively eliminates pressure spikes from the system and ensures that the slurry flow from the pumping apparatus remains constant and is matched to the water flow rate of the pump 142.

The invention holds a number of benefits. The construction of the pumping apparatus is simplified compared, for example, to the pumping system described in the aforementioned international application. On-site requirements are reduced primarily because construction and assembly take place essentially under factory conditions. Through the use of three pump units the pumping rate, compared to the pumping system in the aforementioned international application, is effectively doubled.

Further benefits include the following, some of which have already been referred to:

-   -   The slurry supply source 102 (152 in FIG. 13), only needs to be         slightly higher than the pump units.     -   As the containers to which the components of the pumping         apparatus are mounted, and which are used for transport         purposes, are, for practical purposes, conventional containers,         the shipping and transport thereof can be accomplished on a         worldwide basis using standard techniques.     -   Within each pump unit the respective bladder is protected         against on-stream slurry or water pressure losses. By way of         contrast in the pumping system described in the international         application referred to, if there is a downstream slurry         pressure loss at least one of the bladders, which is filled with         water, would, inevitably, be destroyed in that it would not be         surrounded and supported by slurry inside the pressure vessel.     -   Maintenance of the components in the pumping apparatus can be         effected at ground level.     -   The water in the apparatus is returned to the water tank 106 (or         140). This tank thus acts only as a buffer. The arrangements         shown in FIGS. 7 and 13 establish a net positive suction head         for the pump which means that possible cavitation conditions for         the pump are for practical purposes eliminated.

In the preceding description reference has been made to the non-return valve 62 and 64. In a preferred embodiment of the present invention each non-return valve 62, 64 is of the kind described in the specification of international patent application No. PCT/ZA2012/000005. 

1. A pump unit comprising: an elongate tubular housing with an inner surface, an inner bore, a first end and an opposing second end, an elongate flexible bladder of tubular form with an outer surface, an interior, an inlet, at one end of the bladder, to the interior, and an outlet, at an opposing end of the bladder, from the interior, wherein the bladder is positioned inside the bore with the bladder in sealing engagement with the housing at opposed ends of the bladder whereby the inlet is in communication with the first end of the housing, the outlet Is in communication with the second end of the housing and an operating volume of variable size is formed between the outer surface of the bladder and the opposing inner surface of the housing, a port for an actuating fluid which is provided on the housing in communication with said operating volume, an inlet non-return valve connected to the first end of the tubular housing, an outlet non-return valve connected to the second end of the tubular housing, a first control valve for controlling the flow of the actuating fluid through the port into the operating volume, and a second control valve for controlling the flow of the actuating fluid from the operating volume through the port.
 2. The pump unit according to claim 1, wherein the elongate tubular housing is a pipe with opposing first and second ends which are flanged and opposing ends of the bladder are sealingly engaged with respective flanges at the first and second ends of the pipe.
 3. The pump unit according to claim 1, wherein the inlet non-return valve allows the medium which is to be pumped to move, under gravity action, into the interior of the bladder.
 4. The pump unit according to claim 1, wherein the outlet non-return valve is adapted to allow the medium which is pumped to pass, under pressure, into a discharge line.
 5. The pump unit according to claim 1, further comprising a bi-directional flow meter for metering the flow of the actuating fluid through the port.
 6. The pump unit according to claim 5, further comprising a controller which is connected to the flow meter and which monitors the volume of actuating fluid which flows into the operating volume, and out of the operating volume.
 7. The pump unit according to claim 1, further comprising a plurality of sensors at respective axially spaced locations on the tubular housing, each sensor providing a respective signal which indicates the proximity of the bladder to the respective location of the tubular housing.
 8. A Pumping apparatus comprising three pump units, each pump unit being according to claim 1, wherein the three pump units are mounted substantially parallel to each other on supporting structure, and wherein with the supporting structure on a level surface, the first ends of the tubular housings are elevated so that each housing then slopes downwardly over the length of the supporting structure towards the second end.
 9. The Pumping apparatus according to claim 8, wherein the first non-return valves and a first manifold are, in use, positioned so that they lie outside the supporting structure and the second non-return valves and a second manifold, in use, lie outside the supporting structure.
 10. A method of operating the pumping apparatus of claim 8 wherein, in sequence: pumping a medium from a first pump unit and, at the same time, preparing a second pump unit for pumping, pumping the medium from a third pump unit and the preparation of the second pump unit is completed. preparing the first pump unit for pumping is preparing the first pump unit is completed and the preparation of the third pump unit for pumping is commenced. 